Chorus effects systems



Oct. 1957 A. B. FREEMAN CHORUS EFFECTS SYSTEMS 2 Sheets-Sheet 2 Filed Sept. 18, 1964 PEG. 5

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flL% d 1 44 4/ 1 United States a Patent 3,347,973 CHORUS EFFECTS SYSTEMS Alfred B. Freeman, North Bergen, NJ. (8720 Skokie Blvd, Skokie, 111. 60076) Filed Sept. 18, 1964, Ser. No. 397,517 16 Claims. (Cl. 84-114) ABSTRACT OF THE DISCLOSURE An electronic musical instrument apparatus for producing chorus effects uses combinations of octave and non octave frequency dividers in its tone generators. A tone generator set using chains of divide by three circuits in combination with a conventional tone generating set using octave dividers produces useful chorus effects over awide frequency range. Voltage responsive tuning means permits the player to shift the tuning of one set with respect to the other and so vary the rate of beating.

sicians playing the same note on the same kind of instru-.

rnent. The explanationof the resulting beauty of their composite tonality. resides in the fact that the musicians inadvertently play at slightly different pitches. The result is an interesting and pleasing tonal undulation. These in-,

advertent differences in pitch, while productive of a very noticeable change in quality, are. actually very small, their mutual deviation factor being of a fraction of a percent.

In pipe organs, different tone generating elements are used for different voices and the tuning of the different elements inadvertently vary somewhat. Sounding voices together in ensemble-therefore results in chorus effects. In addition, the celeste voice for pipe organs uses two or more ranks of pipes which are deliberately detuned from each other to enhance the effect. Such effects are noticeably lacking in electronic organs employing a single set of tone generators and particularly in those in which generators for the same note in different octaves are locked together in frequency. Multiple sets of-tone generators with non-locked octaves have been used in expensive electronic organs to obtain these effects. In addition to being expensive, these past systems pose problems in obtainingand maintaining the desired tuning relations and have limitations on the variety of effects which can be obtained without excessive expense.

The instant invention provides a variety of such effects at a reasonable cost. One set of tone generators of this invention uses chains of frequency dividers with factors of rather than A as in conventional systems providing locked octave relations. This permits stretched octave tuning similar to that used in sets with independent generators. The slightly imperfect octave intervals provide a chorus effect on ensembles of voices of different footage supplied by the set. In addition, the frequency deviation from a set using octave dividing chains increases in percent with lower octaves to provide a chorus effect between sets which is more nearly optimum than between two octave dividing sets. The optimum pattern of frequency deviation for chorus effects over a range of several octaves is one which produces tonal undulations with Patented Oct. 17, 1967 a rate that is a non-linear function of frequency. W. C. Wayne, Jr. lists what he considers an optimum pattern in US. Patent No. 3,004,460 issued Oct. 17, 1961.

In addition, the invention provides means for shifting the tuning of all generators in a set by the same percent with sufficient accuracy for fine musical effects. This allows the player to vary the chorus effects between two or more sets of generators to achieve different musical results. It further permits quartertone relations to be established between notes played on different manuals when desired. Still further, the means can be used for obtaining glissando effects and for applying asynchronous vibrato to generators which are otherwise highly stable in fre-.

quency. The invention also provide systems with other non-octave frequency dividing stages for obtaining chorus effects economically and means for obtaining added utili-' zation of multiple sets of tone generators.

An object of the invention is means for'economically providing chorus effects in electronic musical instruments. A further object of the invention is 'means for providing chorus effects in electronic musical instruments which can be varied by the player.

A still further object of the invention is means for using multiple sets of tone generators for producing chorus effects in other ways to further add to the musical resources of the instruments.

A yet further object of the invention is means for shifting the frequency of all of a set of generators by the same percent in a manner suitable for obtaining glissando effects and synchronous vibrato and for establishing quartertone relations and a variety of chorus effect relations with other sets of generators.

A further still object of the invention is a tone generating system for electronic musical instruments using frequency divider chains which intervals.

Other objects and advantages together with a fuller" understanding of the invention will be had by referring to the following specification taken in conjunction with the accompanying drawings in which:

I FIG. 1 is an overall block diagram of an embodiment of the invention.

FIG. 2 is a partial schematic and partial block diagram of a differential tuning means which may be'used with the embodiment of FIG. 1.

a FIG. 3 is a partial schematic diagram of tone distribution which may be used for the embodiment of FIG. 1.

system which is part of the invention.

FIG. 6 is a schematic diagram of two frequency dividing stages which may be used with the tone generating system of FIG. 5.

FIG. 7 is a chart of the frequency relations which are preferred for the tone generating system of FIG. 5.

FIG. 8 is a detailed block diagram of tone generators illustrating another system which may be used in the embodiments of FIGS. 1 and 4.

FIG. 9 is a chart of the frequency differences between notes provided by different non-octave and octave divider chains.

Referring now to FIG. 1, master oscillator set 11 and 12 provide outputs via cables 13 and 14 respectively to their respective frequency divider sets 15 and 16 and to T instrument playing controls and output apparatus 17.

remaining equipment necessary for using the tone signals provides non-locked V octave:

received to produce music such as keyboards, stops, tone shaping networks, amplifiers, and an electrical signal to sound transducer.

Differential tuning means 20 connects to oscillator set 12 via cable 21 and receives a control voltage from apparatus 17 via line 22. Tuning means 20 produces the same-percent shift in frequency of all oscillators in set 12 with the percent being a function of the voltage on line 22. It is thus possible to controllably vary the frequency difference between the tone signals provided by oscillator set 12 and divider set 16 and those provided by oscillator set 11 and divider set 15. The player can thus obtain a wide variety of chorus effects between tones from the .two pair of sets. The frequency difference can also be set for such relations as a quartertone spacing between the two pairs for special effects when played together from two different manuals.

Apparatus 17 can also supply a voltage changing under control of the player for a glissando efiect on the outputs of sets 12 and 16. Apparatus 17 may further include a five toseven cycle per second oscillator whose output can also be applied to line 22 for a synchronous vibrato. Application of vibrato through tuning means 20 has the advantage of making it possible to use oscillators in set 12 which are otherwise very stable in frequency. It will be recognized that a similar tuning means could also be provided for oscillator set 11 to obtain the same effects on its outputs and those of divider set 15.

Oscillator sets 11 and 12 may consist of any number of any type of oscillator suitable for musical purposes and adaptable to a tuning means 20. A preferred form will be discussed later. Divider sets 15 and 16 may each consist of conventional chains of octave dividers of various types but such would provide a constant percent frequency difference in all octaves. It is preferred that one be made up of non-octave dividers to provide a varying percent difference in different octaves as will also be discussed later. Divider sets 15 and 16 may also each consist of various combinations of octave and non-octave dividers to provide a greater variety of chorus effects and increased tonal resources.

Referring now to FIG. 2, oscillators 23a and 23b are two of .a set such as may be used in oscillator set 12 of FIG. 1. The normal frequency determining components consist of the parallel combinations of coil 24a and capacitor 25a and of coil 24!) and capacitor 25b re spectively. These are 'part'of oscillators 23a and 23b but are shown separately for convenience of discussion. Oscillators 23a and 23b are of a Hartley type such as is widely used in electronic organs and may employ either a vacuum tube or transistor as the active element. The design used may be one with a very high frequency stability as it need not be variable in frequency in response to a varying bias voltage for vibrato effects as is necessary in some organs.

Capacitor 26a connects to the ungrounded junction of coil 24a and capacitor 25a via one line of cable 21. The other side of capacitor 26a connects to the junction of diodes 27a and 28 which are connected in series between ground and line 22. Line 22 is effectively shorted to ground for signals in the frequency range of oscillators 23a and 23b by capacitor 29. Line 22 connects through resistor 30 and the arm of multiposition switch 31 in the position shown to the arm of potentiometer 32. Other positions of switch 31 connect line 22 through resistor 30 to the junctions of resistors 33 and 34 and of resistors 34' and 35. Line 22 may also be connected to vibrato oscillator 36 by switch 37. Capacitor 26b and diodes 27b and 28b are connected to oscillator 23b similarly to the manner in which capacitor 26a and diodes 27a and 28a are connected with respect to oscillator 23a.

Controlling the voltage on line 22 effectively controls the portions of the cycles of oscillators 23a and 23b for which capacitors 26a and 26b are effectively in the circuit. The greater the portion of the cycle for which they are effective, the greater the frequency shift produced. If line 22 is grounded, for example, diodes 27a and 27b conduct on negative going portions of the cycles and diodes 28a and 28b on positive going portions so capacitors 26a and 26b are essentially in parallel with capacitors 25a and 25b respectively. If line 22 is positive, neither of diodes 27a and 28a and diodes 27b and 28b will be conducting for a portion of the cycles and capacitors 26a and 26b will be effectively disconnected during these intervals.

If the amplitudes of signals of all oscillators are the same, the relative sizes of each capacitor pair, such as capacitors 25a and 26a, determine the frequency shift for a given voltage change on line 22. These can be selected to give the same percent frequency change for the same voltage change for all oscillators. If the amplitudes of oscillation are different, variation of the size of the capacitor, such as capacitor 26a, can be made to compensate to obtain satisfactory tracking. Transistor oscillators may be preferred to avoid changes of amplitude with aging. The frequency shift necessary for a wide range of chorus effects is of the order of 0.5% while a shift of approximately 3% is necessary to establish quartertone relations.

The use of switch 31 to select voltages either from the arm of potentiometer 32 or the voltage divider chain consisting of resistors 33, 34, 35 permits and continuously variable adjustment or quick selection of preset values of certain frequently used effects. Resistor 30 is used for isolation so that line 22 can always be driven by the output of vibrato oscillator 36 through switch 37. For controlled glissando as Well as other effects, it is advantageous to use a foot operated device for potentiometer 32. Various other control arrangements would also be satisfactory and additional effects might be provided.

Referring now to FIG. 3, cables 18 and 19 from divider sets 15 and 16 respectively of FIG. 1 connect to switches 40 and 41 respectively. Each pair of switches 40 and 41 are mechanically coupled to a playing key 42 and are located so they will contact busses 43 and 44 respectively when it is operated. Cables 18 and 19 are also shown conneeted respectively to switches 45 and 46 which are also mechanically coupled to playing keys 47 for selective engagement with busses 48 and 49 respectively. Resistors in series with each switch are required but not shown and it w6ill be assumed that they are part of divider sets 15 and 1 While only a few keys 42 and 47 are shown, it will be recognized that any number could be provided and that 7 this is a standard arrangement for an electronic organ with upper and lower manuals except that alternate busses are supplied from alternate generator sets. Busses 43, 44, 48, and 49 each supply signals to different stops and tone forming networks which can be selected for sounding by the player as desired. Chorus effects can thus be obtained between different voices played by the same manual or between manuals. If signals from the two sets of generators were premixed it would only be possible to get tones without chorus effects by adjusting both sets to the same frequency as could be done by the apparatus of FIG. 1. The pairs of busses 43 and 44 and busses 48 and 48, and 49 each supply signals to different stops and tone footages depending upon the tonal resources desired and as many extra sets of busses as desired can also be pro vided. Quartertone relations between the notes played on the two manuals can be provided by adjusting the generator sets and using stops on each manual from one generator set different from those used on the other.

Referring now to FIG. 4, master oscillator set 50 may be the same or similar to oscillator sets 11 or 12 of FIG. 1. Oscillator set 50 provides outputs via cable 51 to frequency divider sets 52a and 52b which in turn provide outputs via cables 53a and 53b respectively to output and controls apparatus 54 which may be the same as apparatus 17 of FIG. 1. Divider sets 52a and 52b form a combination which might also be used as divider sets 15 or 16 of FIG. 1. Frequency divider set 52a will include at least one n-on-o'ctave' dividing stage in each chain. Frequency divider set 5212 may consist only of octave dividing chains or may employ a non-octave stage in each chain which is different or in a different location in the chain than that of divider set 52a. Chorus effects will then be produced between signals from the different divider sets 52a and 52b.

One of the several combinations which may be used for the apparatus of FIG. 4 is shown in FIG. 5. Refer-ring now to FIG. 5, master oscillator set 55 consists of 19 oscillators 56 tuned to produce notes running from C1 to F#2 as indicated. The number in these and the following note designations indicates the octave starting with one for the highest and counting down. The outputs of oscillators 56 drive the first stages in the chains of divider set 57. Dividers 58 in set 57 normally divide their incoming frequencies by three but some can also be switched to divide by two for special purposes to be discussed later. The twelve highest frequency oscillators 56 also drive the first stages of frequency divider set 59 which consists of twelve chains of octave dividers.

When dividers 58 are dividing by three, the notes produced are those indicated in the blocks without parenthesis. The note produced by each divider 58 is a perfect fifth and octave below the note of the preceding stage as a natural consequence of dividing by three. To provide equal intervals between all adjacent notes, it is necessary that oscillators 56 be tuned for an interval factor equal to the 19th root of /3 rather than the Equal Temperament interval of the 12th root of /2. The relations to the top note, C1, are then shown in the chart of FIG. 7. The difference between F #2 and F2, which must equal C1, is then the same as for the others and the same factor holds for all other notes produced by dividers 58.

With this type of scale, the fifths will be flat by approximately 0.08% from a perfect fifth which is closer than the Equal Temperament fifth which is flat by approximately 0.12%. The octaves will be sharp by approximately 0.08% from a perfect octave. A stretched octave tuning, such as this, is preferred in instruments having independent tone generators. Chorus effects are then obtained be tween the' same notes in different octaves and so also between voices of different footage supplied by divider set 57. The frequency difference between the signals for the same notes produced by divider set 57 and by divider set 59 will increase progressively at a rate of 0.08% per octave going toward the base. The beat, or tonal undulation rate, between the two will thus be substantially constant over the entire frequency range.

The optimum pattern of frequency difference with frequency for chorus effects appears to lay somewhere between one which will produce a uniform beat, or tonal undulation, rate and one which will produce a rate proportional to frequency. Patterns within this region can be provided by the apparatus of FIG. 1 if divider set 15 consists of a divide by three systems such as divider set 57 and divider set 16 consists of an octave divider set. Oscillator set 11 would then preferably be the same as oscillator set 55. The frequency difference pattern would then be formed by the sum of the adjustable percent difference in frequency between oscillator sets 11 and 12 and the 0.08% per octave increments provided by the divide by three system.

The voltage on line 60a can be switched by control source 61 to change the first stage dividers 58 to which it connects from divide by three to divide by two. Switching the voltage on line 60b by control source 61 causes the following stage dividers 58 to continue to divide by three from the new frequency received from their preceding stages. The notes produced by dividers 58 will then be those shown in parenthesis in the blocks. The result is a shift of all outputs of dividers 58 in set 57 upward by a fifth. The voices using these outputs for a particular footage will then be shifted upward by a fifth for a Quint and so provide a different musical effect. The

6 shift could also be made downward by a fourth by changing the first stage dividers 58 to divide by four. Change to division by five would likewise shift downward by a sixth interval. Such changes could also be used with a system normally divided by octaves. A suitable divider circuit for making such changes is shown in FIG. 6.

Referring now to FIG. 6', unijunction transistors 62a and 62b have their base ones connected to ground and their base twos connected through resistors 63a and 63b respectively to positive supply 64. Capacitors 65a and 65b connect between the respective emitters and ground. Resistors 66a and 66b connect the emitters of transistors 62a and 62b to supply 64 when switch 67 is in the position shown. When switch 67 is in the other position, resistor 66a connects to supply 68a and resistor 66b to supply 68b. Output tone signals are taken from the emitters through resistors 69a and 69b. Master oscillator 70 provides negative going pulses through capacitor 71a to base two of transistor 62b. Capacitor 71b interconnects the base twos of transistors 62a and 62b while capacitor 71c may interconnect base two of transistor 62b with the base two of a following stage.

This provides two stages of sawtooth oscillators with capacitors 65a and 65b charging through resistors 66a and 66b respectively and discharging through transistors 62a and 62b respectively when the firing points are reached. A negative going voltage on base two lowers the firing point so the oscillators can be synchronized by the pulses through capacitors 71a and 71b at frequencies near their natural frequency. The pulse through capacitor 71b will be considerably larger when transistor 62a conducts. Selection of capacitors 65a and 65b in combination with resistors 66a and 66b for natural frequencies slightly lower than the operating frequencies desired allows both circuits to synchronize at sub multiples of the frequency of oscillator 70.

The natural frequency of the oscillators provided by transistors 62a and 6221 can be changed by changing the voltage to which resistors 66a and 66b connect. Switching resistors 66a and 66b to supplies 68a and 6812 respectively causes the oscillator provided by transistor 62a to synchronize at a different sub multiple of oscillator 70 and the one provided by transistor 62b to synchronize at the same sub multiple of the new frequency received from its preceding stage. The arms of switch 67 also conmeet to lines 72a and 72b to which stages in other chains canbe connected for corresponding changes. The same means could also be used with other types of synchonizing relaxation oscillators for various frequency dividing factors. A greater range of factors in sets of the present type can be obtained if all transistors in the stages to be changed have substantially the same firing and valley points. Capacitors 71a, 71b and 710 should be as small as practical for good triggering to avoid back coupling effects.

Referring now to FIG. 8, master oscillator drives the first stages of-two divider chains, one consisting of dividers 81a, 81b, and 810 and the other of 82a, 82b and 82c. Additional stages may be added to either or both chains. One or both-of first stage dividers 81a and 82b will be non-octave dividers while other stages may be either octave or non-octave dividers. One possible combination already illustrated in FIG. 5 was to have one chain of divide by three circuits and the other of octave dividers. Other combinations can consist of either of the aforegoing types for one chain and another starts with a first stage divider dividing by five and follows with octave dividers. Other combinations may also be found useful in providing multiple sets of tones from a single master oscillator set.

FIG. 9 shows the percent deviations provided by various first stage dividing ratios from the corresponding octave divided Equal Temperament notes. The division by five mentioned above would provide notes sharp by 0.8% from those of an octave chain and by a progressively greater amount from a divide by three chain. A divide by seven first stage would likewise provide'notes sharp by 1.75% while those from a divide by eleven stage would be nearly a quartertone sharp. The difference between notes of chains with different ones of these dividing factors can be estimated by taking their difference in percent from the Equal Temperament notes. The note designations shown in the chart are those which would obtain if the master oscillator were tuned for C1.

Octave divider sets may consist of circuits providing either a sawtooth or squares waveform. Non-octave divider sets will more conveniently consist of circuits providing sawtooth waveforms. In instruments using multiple sets of dividers such as those of FIGS. 1 and 4, it will be advantageous to use an octave dividing set which produces square waves. The sets can then be divided between the dilferent voices to provide each voice with the waveform which is most effective for it.

While the present invention has been described in conjunction with some specific embodiments, it will be recognized that various changes and modifications can be made without departing from the spirit and scope of the invention as set forth in the following claims.

What is claimed is:

1. In an electronic musical instrument, a first set of tone generators, a second set of tone generators, a set of voltage responsive tuning elements connected individually to the master oscillators of one of said sets, a voltage source connected to said voltage responsive elements and adjustable by the player to shift the tuning of said oscillators, and means for translating the outputs of said generators into sound.

2. The combination according to claim 1 wherein is included a fixed voltage point and wherein said voltage responsive tuning elements each comprise a reactance and means for switching said reactance out of effect for voltages between said fixed voltage point and the output of said controllable voltage source.

3. In an electronic musical instrument, a first set of tone generators, a second set of tone generators including master oscillators non octave frequency divider stages, means for shifting the tuning of one of said sets of tone generators by the same percentage responsive to the player, and means for translating the outputs of said generators into sound.

4. The combination according to claim 3 wherein the frequency dividers for said second set of tone generators consists of divide by three stages arranged in chains.

5. The combination according to claim 4 wherein there are 19 of said chains of divide by three stages wherein there are 19 master oscillators driving the first stages of said chains in said second set of tone generators.

6. The combination according to claim 5 wherein said 19 master oscillators are tuned to a factor of difference between each successive pair equal to the 19th root of three.

7. The combination according to claim 3 wherein is included means for switching the division factor of some stages of said frequency dividers.

8. The combination according to claim 3 wherein said shifting means can move the tuning of said first set of tone generators for a quartertone relation with said second set and including two manuals and means for playing tones from one of said sets of tone generators from one of said manuals and tones from the other of said sets of tone generators on the other of said manuals.

9. In an electronic musical instrument, a set of tone generators, a controllable voltage source, a set of reactances individually associated with the frequency determining portions of said tone generators, and means for switching said reactances into effect on said tone generators only when the signal voltage from their respective one of said generators is on one side of the output of said controllable voltage source.

10. The combination according to claim 9 including a fixed voltage source and wherein said means for switching comprises a first set of diodes connected to said fixed voltage source and individually to said reactances, a second set of diodes connected to said controllable volt age source and individually to said reactances in opposite polarity to said first set.

11. A tone generating set for electronic musical instruments comprising a set of master oscillators and a set of frequency dividers arranged in a plurality of chains with the first stage in each chain being driven by one of said oscillators and wherein each of said chains include a non-octave dividing stage, and means for translating the outputs of said tone generating set into sound.

12. The combination according to claim 11 wherein said set of master oscillators consist of 19 oscillators and said set of frequency dividers consists of divide by three stages arranged in 19 chains.

13. The combination according to claim 12 wherein said 19 master oscillators are tuned to a factor of difference between each successive pair of the 19th root of three.

14. A tone generating set for electronic musical instruments comprising a set of master oscillators, a first set of frequency dividers arranged in chains, a second set of frequency dividers arranged in chains and including at least one non-octave dividing stage in each chain, means for connecting individual ones of said oscillators to drive a chain from each of said first and second sets of frequency dividers, and means for translating the outputs of said tone generating set into sound.

15. A tone generating system for electronic musical instruments comprising a set of master oscillators, a set of frequency dividers arranged in a plurality of chains with the first stage in each chain being driven by one of said oscillators, means for switching the division factors of one stage in each chain from one value to another, and means for translating the outputs of said tone generating system into sound.

16. The combination according to claim 15 wherein the stage in each chain which is shifted is of a relaxation oscillator type synchronizable at frequencies near its natural frequency and wherein said switching means comprises means for changing a voltage supply controlling the natural frequency of stages connected to it to be shifted.

References Cited UNITED STATES PATENTS 3/1950 Hanert 841.24X 5/1966 Wolfanger 84-124 

3. IN AN ELECTRONIC MUSICAL INSTRUMENT, A FIRST SET OF TONE GENERATORS, A SECOND SET OF TONE GENERATORS INCLUDING MASTE OSCILLATORS NON OCTAVE FREQUENCY DIVIDER STAGES, MEANS FOR SHIFTING THE TUNING OF ONE OF SAID SETS OF TONE GENERATORS BY THE SAME PERCENTAGE RESPONSIVE TO THE PLAYER, AND MEANS FOR TRANSLATING THE OUTPUTS OF SAID GENERATORS INTO SOUND. 